Since the advent of mail delivery, one of the duties associated with mail delivery has been the sorting of mail by the individual mail carrier into a sequence corresponding to the stops on his particular mail route. This has often been a very time-consuming procedure which can take up to half a work day. It is desired then to provide a means for sorting the mail faster, thus providing the carrier with more time to deliver mail.
In recent years, attempts to automate the postal service have taken a number of forms. For example, machines such as the multi-line OCR, the 880 bar code sorter (BCS), and the delivery bar code sorter (DBCS) have been provided to sort mail. Typically, these machines now sort mail by zip code or by bar code corresponding to the zip code. Only recently have attempts been made to provide carrier sequence bar code sorting with an intent to facilitate mail handling functions.
Carrier sequence bar code sorters have been described in U.S. Pat. Nos. 5,097,959 and 5,097,960 to Tilles et al. These patents are directed to a multiple-pass, sorting machine. This type of machine sorts mail into stackers which fill in a top down sequence with the mail from a previous pass retained at the bottom of the stacker. In one of such patents, a single recirculating vehicle empties the bottom of each stacker individually and indexes along a track for recycling for a further pass. In the second of said patents, multiples of such vehicles are provided for each stacker. Typically, in such a machine, a wide area bar code reader (WABCR) is used. A singulator is also used upstream of the WABCR to arrange the mail individually, and a leveler which is used to align the mail for reading. Once the mail is read, the bar code information is interpreted by a microprocessor and the mail assigned to a particular stack. Also, in U.S. Pat. No. 5,119,954, a multi-pass sorting machine is provided which uses two passes only. In order to meet the normal carrier requirements, this machine requires a minimum of 32 or up to 50 vertical stackers for the mail being sorted. As will subsequently be described, 32 stackers in a two-pass system should be capable of sequencing mail for 1,000 stops. In both patents, the zip code used is an 11-digit zip code which is capable of identifying the carrier's individual stops.
Sorting mail then would mean separating the mail into a vertical stacker for each stop. This could mean, for a typical route, up to 1,000 stackers. However, to sequence the mail, multiple stops will be retained within a single stacker, with the stops in each stacker retained in sequence. By sequencing, the number of stackers required can be reduced.
The number of stackers required will be related to the number of stops and reduced by the number of passes. Accordingly, the number of stackers raised to the power of the number of passes is equal to the number of stops. In this way, a system having 32 stackers which uses two passes would be capable of handing 1,024 stops.
There is a need then to provide a carrier sequence bar code sorter machine which can be operated by the individual mail carrier and which is capable of sequencing the mail in the carrier's route automatically which, in turn, requires the capability of sequencing the mail for 1,000 stops. There is also a need to provide a machine which is compact and suitable for installation at individual postal delivery units. Accordingly, the machine must provide multiple passes and, preferably, would achieve multiple pass sequencing to completion without the need for intermediate sweeping. Sweeping, or unloading, is the manual removal of the mail from the stackers. Obviously, it is desirable to minimize the physical handling of the mail and limit the same to a single sweep at the end of the sequencing operation.